A regular garage compressor doesn't produce enough pressure to be useful in PCP's . Even what is considered to be a low operating pressure pcp such as the new discovery uses 1500-2000psi . As far as leaving them pressurized ; They are designed to be stored under pressure , although I wouldn't recommend leaving one at max pressure for extended periods of time. A guy at our field target club brought a rifle that had been stored for several years that showed to be still pressurized . He topped off the airtube on the rifle and shot it , to check it out . it shot the same as it did when put away almost 10 years before. kirby